Magnetic core



March 21, 1933. 0. IDAHL ET L 1,902,491

MAGNETICCORE Filed Nov. 11, 1932:

Inven tors Otto Dah I, Joachim FFaf'f'enber" er,

The i 1* At corney.

Patented Mar. 21, 1933 UNITED,- STATES PATENT OFFICE OTTO DAHL, OFIBERLIN-WILMERSDORF, AND J'OACHIM IPFAIFENBERGER, F BERLIN- MARIENDOBF,GERMANY, ASSIGNORS '10 GENERAL ELECTRIC COMPANY A CORPORA- TION OF NEWYORK MAGNETIC GORE Application filed November 11, 1932, Serial No.642,306, and in Lermany November 12, 1931.

Our invention relates to magnetic cores such as are used in smalltransformers, reactors and the like, and its general object is toprovide an improved method for producing a magnetic core of this generaltype.

Magnetic cores have already been produced by rolling or coiling a stripof magnetic sheet material into annular form. This method of forming amagnetic core is of advantage in that there' is little or no wastematerial and the strip may be easily produced with the grain of thematerial extending lengthwise of the strip and therefore in thedirection of the magnetic flux in the finished core. In

16 forming these strip cores according to the previous practice,however, there has been the disadvantage, particularly in the case ofcores of small diameter, that the strips of ma etic material forming thecore have been un or elastic stresses which affected adversely themagnetic properties of the core and particularly the hysteresis losses.

The present invention provides a process for producing a magnetic coreformed by.

winding or coiling a strip of sheet magnetic material in such mannerthat the magnetic properties of the core are not affected by any elasticstresses in the core material.

The invention will be better understood from the following descriptiontaken in connectioh with the accompanying drawing in which Fig. 1 is aperspective view of a strip of magnetic sheet material which has beencoiled or wound into annular form, and Fig.

5 2 is a diagrammatic perspective view of a transformer including thefinished core and primary and secondary winding. Similar referencecharacters indicate like parts in both figures of the drawing.

In forming a magnetic core in accordance with the present invention, astrip of magnetic sheet material 10 is first wound into annular form, asshown in Fig. 1, to a diameter considerably smaller than the desired 4diameter of the finished core. The coiled strip is then permitted toexpand to the desired diameter, as shown in Fig. 2. The outer end of thestrip 10 may be held in place by small spot welds 11. In some cases itmay be desirable to wind the strip 10 and allow it to expand while it-isheated to a temperature of from 100 to 350 C. The ,completed core may beprovided with primary and secondary windings 12 and 13 respectively.

The invention has been explained by describing the process of formingthe particular magnetic core shown in the drawing, but it will beapparent that changes may be made without departing from the spirit ofthe invention or the scope of the appended claims.

What we claim as new and desire to se cure by Letters Patent of theUnited States 1. A method for making an annular magnetic core, saidmethod including the steps of winding a strip of magnetic sheet materialinto annular form and to a diameter smaller than the desired diameter ofthe finished core, and then permitting the wound strip to expand to thedesired diameter.

2. A method for making an annular magnetic core, said method includingthe steps of heating a strip of magnetic sheet material to a temperaturebetween 100 and 350 0., winding the stripof magnetic sheet material intoannular form while still heated and to a diameter smaller than thedesired diameter of the finished core, and then permitting the woundstrip to expand while still heated to the desired diameter.

In witness whereof, we have hereunto set.

